The invention relates to a method and apparatus for cooling and for further treatment of hot white cement clinker which is sprayed with water after leaving the clinker calcining kiln, whereupon the white cement clinker is dried under contact with a gas stream.
In all methods for the manufacture of cement clinker employing a rotary tubular kiln, the cement clinker has a temperature of nearly 1400.degree. C. when it emerges from the rotary tubular kiln and must be cooled down to about 100.degree. C. through 200.degree. C. for further handling, and such cooling is normally undertaken with cold cooling air. However, in the manufacture of white cement clinker, air cannot be employed as coolant since the oxygen contained therein oxidizes the metallic components of the clinker. It is this oxidation state which produces the coloring of the cement clinker, for example gray coloring in various gradations, and the discoloration of the cement clinker depends on the quantity and the quality of the metallic components present in the clinker.
In order to protect against undesired oxidation phenomena, it is known to protect white cement clinker against exposure to oxygen when it is cooled (German Patent No. 25 44 343). For that purpose, the hot, sintered white cement clinker is first sprayed with a reduction agent such as, for example, oil when it departs the rotary tubular kiln and is subsequently cast into a water bath after it departs the rotary tubular kiln. This water bath is contained in cells of a rotating drum, and the white cement clinker quenched in the water bath is additionally sprayed with cooling water from above. As a consequence of the water bath cooling, the quenched white cement clinker has a water content of about 10% through 16%, or even higher when the clinker is fine-grained. This high water content leads to a reduction of the strength values of the cement manufactured of such white cement clinker, since a certain hydration is unavoidable, particularly when fine-grained clinker particles are present. In the known method, the quenched white cement clinker high in water content is dried with the assistance of a cooling air stream and with the expenditure of a relatively high thermal energy before the clinker can be ground. In this known method, moreover, the risk exists that a part of the water vapors generated from the cooling water will enter into the rotary tubular kiln and reduce the flame temperature and the sintering temperature therein. In the final analysis the energy balance is deteriorated, the energy requirement in the rotary tubular kiln is increased, the economic feasibility of the known method is diminished and, as a total consequence thereof, the final product, namely white cement, is made more expensive.
The object of the invention is to create a method and an apparatus for cooling and for further treatment of hot white cement clinker wherein the disadvantageous consequences of quenching the clinker in a water bath are avoided.
A further object is to avoid the deterioration of the performance capability of the clinker calcining kiln due to water vapor and to obtain further advantages.
Another object is that the white cement clinker treated in accordance with the invention should exhibit a high degree of whiteness and the cement manufactured therefrom should exhibit high strength values and should nonetheless be capable of being economically manufactured.
In the method of the invention, the white cement clinker is sprayed with water in an oxygen-free atmosphere and is subsequently conducted in counter-current flow relative to a warm drying gas stream which is withdrawn separately from the cooled, dried, white cement clinker, being withdrawn together with the vapors picked up from the cement clinker. The warm drying gas stream whose principal job is to carry out the vapors constantly developing from the sprayed hot clinker, can be highly enriched with water vapor up to the point it reaches the saturation limit. The hot cement clinker departing the clinker calcining kiln such as, for example, the rotary tubular kiln having a temperature of about 1400.degree. C., is sprayed with such a great quantity of water in a pre-cooling stage such that the cement clinker is cooled shock-like to a temperature of about 500.degree. C. through 800.degree. C. but nonetheless exhibits a moisture content of only about 3% through 9% on a case-by-case basis. Subsequently, the cement clinker pretreated in this way is treated with the warm drying gas stream in a final cooling stage/drying zone, being treated in such fashion that the dry cement clinker departing this zone exhibits a temperature of about 60.degree. C. through 100.degree. C. as well as a residual moisture less than 0.5%. Due to the comparatively low moisture content of the cement clinker pretreated in the pre-cooling stage, about 3% through 9%, for example, about 6%, and due to the short path which the cement clinker traverses between the pre-cooling stage and the final cooling stage/drying zone, the risk of the undesired hydration of the clinker as well as the thermal outlay for drying the clinker are minimized. Thus, white cement clinker having high product quality can be manufactured with the method of the invention, and further can nonetheless be manufactured relatively economically.
In accordance with a special feature of the invention, the hot white cement clinker departing the clinker calcining kiln such as a rotary tubular kiln is circulated and mixed avoiding exposure to the outside atmosphere. It is circulated and mixed in the pre-cooling stage after the water spraying for the purpose of blending the clinker with itself and with the vapors as well as with water residue which may be present. The cooling water employed is distributed to all clinker particles with optimum uniformity and the residual heat remaining in the quenched clinker is as optimumly exploited as possible for the evaporation cooling and simultaneous drying of the clinker, this considerably promoting the economic feasibility of the method of the invention.
An apparatus of the invention for the implementation of the method is characterized by a rotary tube which is subdivided into a co-current flow pre-cooling stage with an admission opening for water-sprayed white cement clinker and into a following counter-current final cooling stage/drying stage with a discharge opening for cooled, dry clinker.
Other objects, advantages and features will become more apparent with the teaching of the principles of the invention in connection with the disclosure of the preferred embodiments in the specification, claims and drawings, in which: